The year 2020 will be remembered as a time of major inflection points, including the coronavirus pandemic and the U.S. election. More obscure to most Americans, but a dire turn in the shaping of the 21st century, is an event that took place in Hong Kong at 11 p.m. on June 30, the eve of the 23rd anniversary of the handover of the former British colony to China.

That event was the imposition of China’s new National Security law for Hong Kong, the communist instrument with which China, in one stunning blow, stripped away wholesale the rights and freedoms it promised to Hong Kong for 50 years after the handover. Written and passed in Beijing, imposed without allowing Hong Kong’s people any say, this law effectively eliminates the institutional barriers that separated Hong Kong’s relatively free and open system from China’s increasingly totalitarian rule. Under this law, virtually any act of choice in Hong Kong is not a matter of right, but done at the dispensation — or not — of Beijing.

Passage of the law marks the first full takedown by a communist tyranny of a thriving and mature free society. For Hong Kong, it is a colossal tragedy. For all of us, it is a harbinger of the 21st century world order that China’s ruler, Xi Jinping, is already heavily influencing and proposes to dominate under his vision of a “shared future for mankind.”

Because Hong Kong falls under Chinese sovereignty, China calls its crushing of Hong Kong a purely internal matter. That’s wrong. China signed a binding international treaty with Britain, the 1984 Sino-British Joint Declaration, guaranteeing that from the time of the 1997 handover until at least the year 2047, Hong Kong would be self-governing in domestic affairs, enjoying a “high degree of autonomy” under an arrangement Beijing dubbed “One Country, Two Systems.”

What stands out today is not solely China’s bad faith in violating a binding treaty that still had 27 years left on clock — though that should give pause to anyone inclined to believe such worthless declarations by Beijing, as its promise to reduce carbon emissions to zero by the year 2060. The further alarming precedent is the speed, brutality and sweep with which China has reduced the vibrant, open city of Hong Kong to a shrouded enclave of repression, censorship and political prisoners.

In sizing up China’s threats toward its next target, Taiwan, and its likely timetable for Xi’s desired dominance worldwide, it is important to understand just how rapidly China rolled over Hong Kong, once Beijing really swung into motion, and how dark a scene it has become. Less than two years ago, Hong Kong was one of the great cities of the free world. It was a cosmopolitan home on the China coast to 7.5 million people, enjoying free trade, free speech, a British legacy of rule of law and great pride in belonging to what their own administration dubbed “Asia’s World City.”

Yes, there were growing portents of big trouble. Beijing had reneged on its promise of genuine democracy, leaving Hong Kong with a chief executive chosen by Beijing, and a chronic pro-Beijing majority in the legislature. Nonetheless, there was a quantum difference between dynamically open Hong Kong and the repressive communist surveillance state of mainland China.

Then, in 2019, Hong Kong’s chief executive, Carrie Lam, tried to bulldoze into force a law allowing extradition to China. Hong Kong erupted in huge street demonstrations, initially against the extradition law, which Lam finally withdrew. The protests quickly turned into demands for democracy and broad defiance of Beijing’s increasingly repressive grip. For months the protests carried on, wreathed in tear gas, with escalating street battles between protesters and police.

Beijing blankly refused to offer any compromise, instead issuing dire threats. Hong Kongers stood their ground. In late November 2019, they seized a symbolic chance to register their desire for democracy by delivering a landslide victory for pro-democracy candidates in district council elections. These are largely powerless posts, but it was at least a chance to cast a vote. That victory raised hopes that in the far more important legislative elections, expected in September 2020, there might be enough pro-democracy votes to finally overcome an electoral system configured to ensure a pro-Beijing majority.

In early 2020 came the spread from Wuhan, China, of the coronavirus. The related restrictions have since doubled as a veil for China’s dirty work. In March, Hong Kong’s government imposed an entry ban on almost all non-residents, now extended through March 2021, drastically curtailing international traffic through the city and effectively walling out many international reporters.

In June, while the world was preoccupied with the pandemic, Beijing delivered its mortal blow to Hong Kong’s freedoms, passing “The Law of the People’s Republic of China on Safeguarding National Security in the Hong Kong Special Administrative Region.”

This law runs to 66 articles, but boils down to Beijing granting itself the power to intervene in Hong Kong in any matter that China’s government deems relevant to national security — a concept that under China’s communist rule means whatever the party overlords want it to mean. The law criminalizes activities such as criticism the authorities deem dangerous, or “collusion” with “foreign elements,” in terms vague enough to put Hong Kongers at risk for what were previously normal discussions. Grave offenders can be sent to mainland China for prosecution and punishment.

The law includes provisions criminalizing “offences” committed not only in Hong Kong, but by anyone, anywhere around the globe. According to a December report submitted to Congress by the U.S.-China Economic and Security Review Commission, “Left unchecked, the law could grant the Chinese government broad power to censor global discourse.”

Under this law, mainland security forces arrived openly for the first time in Hong Kong this summer, empowered to conduct surveillance, warrantless searches and arrests as they see fit. Hong Kong’s authorities began culling pro-democracy books from public shelves. They outlawed the famous protest slogan: “Liberate Hong Kong! Revolution of Our Time!” They banned students from singing or playing the haunting anthem that protesters came up with last year: “Glory to Hong Kong.” When some of Hong Kong’s creative protesters staged a demonstration in which they held up blank placards, they were arrested.

For Hong Kong’s democracy advocates, the legislative elections scheduled for September offered a glimmer of recourse. Hoping to win a majority, they organized primaries in mid-July that produced a record turnout. But the elections never took place. On July 31, Lam announced that due to coronavirus concerns, the elections would be postponed — for a full year.

That left the old legislature in place, with pro-democracy lawmakers in the minority. But even that was too much dissent for Beijing. In November, on grounds of “national security,” the Standing Committee of China’s National People’s Congress disqualified four of Hong Kong’s pro-democracy lawmakers. In protest against the hopelessly stacked deck, the remaining 15 pro-democracy lawmakers quit.

Meantime, the arrests and charges have been proceeding apace, populating Hong Kong’s prisons with political dissidents. Since the start of the protests last year, more than 10,000 have been arrested, many of them prior to China’s security law, but all of them (or anyone in Hong Kong, for that matter) now facing a system in which China’s draconian definition of national security is reshaping the rules. Earlier this month, prominent young democracy advocates Joshua Wong and Agnes Chow received prison sentences.

Most famous of Hong Kong’s democratic dissidents, now awaiting trial on multiple charges, is 73-year-old Jimmy Lai. He’s a wealthy businessman, publisher and founder of the hugely popular pro-democracy newspaper Apple Daily. Hong Kong authorities have arrested him a number of times this year, parading him in handcuffs and shackles, ransacking the offices of his newspaper, and finally charging him under the National Security law with colluding with foreign forces, which could translate into a life sentence, possibly served in China.

Hong Kong authorities have issued arrest warrants for a number of dissidents who have fled the city, as well as a warrant for a naturalized American citizen wanted for the “offence” of lobbying the U.S. government to support Hong Kong’s demands for democracy. In August, 12 Hong Kong dissidents tried to flee by boat to Taiwan. They were seized by China’s coast guard and imprisoned not in Hong Kong, but in mainland China, where 10 have now been indicted.

Hong Kong’s administration is revising school textbooks to delete such democratic ideas as separation of powers and replace them with China’s version of “patriotic education.” There are reports of Hong Kong parents afraid to discuss politics in front of their own children, lest school authorities ferret out signs of dissent.

Xi made his plans for Hong Kong quite clear in an October speech delivered in the nearby Chinese special economic zone of Shenzhen. Never mind the immediate cost, Hong Kong — much diminished — is to be mulched into the surrounding Chinese turf Xi calls the Greater Bay Area, integrated into China’s system as a compliant node in his Belt and Road Initiative for trade supremacy and global dominance.

Under President Donald Trump, the U.S. has led the global response to this nightmare, withdrawing Hong Kong’s special trade status, scrapping extradition arrangements and blacklisting some of Hong Kong’s top officials, including Chief Executive Lam. Most important, the Trump administration has roused the world to the dangers compounding out of China, and the administration has begun steering away from the U.S. policies of open-handed trade and engagement that for so many decades enriched and emboldened China’s Communist Party. Anyone in a Biden administration who might be tempted to revert to the old cozy ways should take a close look at the grim landscape Xi has created this year in the once free city of Hong Kong, and the speed with which he did it.